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| Toxicity of Cadmium and Copper to Barley in Presence and Absence of Zinc |
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| KeyWord:EC50; toxic unit（TU）; combined toxicity; antagonism; synergism |
| Author Name | Affiliation | | BAO Lin-lin | College of Resource Environment & Tourism, Capital Normal University, Beijing 100048, China | | WANG Xue-dong | College of Resource Environment & Tourism, Capital Normal University, Beijing 100048, China | | HUA Luo | College of Resource Environment & Tourism, Capital Normal University, Beijing 100048, China |
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| Abstract: |
| Metal toxicity to plants is different in single system from in multiple metal system. Here toxicities of individual Zn, Cd and Cu and Zn-Cd and Zn-Cu mixtures to barley（Hordeum Vulgare） were tested in nutrient solutions. Toxic unit（TU） model was used to evaluate the combined toxicity of mixture metals. EC50s（metal concentration at which root elongation is inhibited by 50%） were 78.01 μmol·L-1, 2.98 μmol·L-1 and 0.64 μmol·L-1 for Zn, Cd and Cu, respectively, indicating that Cu toxicity was much higher than Cd or Zn in single-metal system. In binary metal systems, Cd toxicity to barley was inhibited by Zn at 5 μmol·L-1, and the values of EC50（Cd） increased significantly. TUmix values of Zn-Cd were greater than 1 TU and increased with Zn concentrations, suggesting an antagonistic effect between Zn and Cd at low Zn concentrations. Such antagonism of Zn-Cd was correlated with Zn proportion in the mixture system. At higher concentrations（>5 μmol·L-1）, Zn exerted high toxicity to barley and increased the joint toxicity of Zn-Cd. Additions of Zn showed greater Cu toxicity to barley than Cu alone. EC50（Cu） values were higher in Zn-Cu mixture than in single-metal system and decreased dramatically with increasing Zn concentrations, showing synergistic toxicity of Zn-Cu. TUmix values of Zn-Cu mixture were less than 1 TU. These results suggest that Cd and Cu may have different toxicity mechanisms, and that more attention should be paid to combined heavy metal pollution. |
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